For example, U.S. 2005/0163605 A1 (JP-A-2005-207320) discloses a fuel pump including an impeller, a casing, and a housing. The casing accommodates the impeller, and defines a pump passage together with a cover. The housing is press-inserted with the casing. Fuel is pressurized through the pump passage with rotation of the impeller, so that the fuel is discharged from the fuel pump. The housing includes a large inner-diameter cylindrical portion and a small inner-diameter cylindrical portion being coaxially connected with each other. The small inner-diameter cylindrical portion has the inner diameter less than the inner diameter of the large inner-diameter cylindrical portion. The casing includes a press-inserted portion, an accommodating cylindrical portion, and an accommodating disc portion. The press-inserted portion is press-inserted to the inner circumferential periphery of the small inner-diameter cylindrical portion. The accommodating cylindrical portion is located in the large inner-diameter cylindrical portion, and is opposed to the outer circumferential periphery of the impeller. The accommodating disc portion is opposed to the bottom surface of the impeller on the side of the press-inserted portion.
In recent years, the impeller is jumboized in outer diameter, adapting to increase in flow rate of the fuel pump. It is requested to increase outer diameter of the impeller without increasing the outer diameter of the fuel pump. Therefore, the accommodating cylindrical portion of the casing is reduced in thickness with increase in outer diameter of the impeller. In this structure, when the press-inserted portion of the casing is press-inserted into the small diameter portion of the housing, a substantially center portion of the accommodating disc portion may by convexly deformed toward the impeller. Consequently, the casing and the impeller cannot define a predetermined clearance therebetween.